Process for the production of copolycarbonates with reduced color

ABSTRACT

A method is provided for reducing the color generated during production of copolycarbonate that includes quinone-type residues. The method includes the steps of mixing the precursors of monomer residues, a carbonate source and a polymerization catalyst into a reaction mixture. The method further includes the steps of introducing an antioxidant such as a hydroxycarboxylic acid to the reaction mixture in an amount sufficient to reduce color formation and introducing the reaction mixture to a series of process units wherein the reaction mixture polymerizes. The resulting copolycarbonate has improved color as compared to a copolycarbonate formed in a process without the step of introducing an antioxidant to the melt polymerization process.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No. 60/540,414 filed on Jan. 29, 2004, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Polycarbonate is a thermoplastic that has excellent mechanical properties such as impact resistance, heat resistance and transparency. Polycarbonates are widely used in applications ranging from football helmets to automobile parts to transparent security windows. More recently, polycarbonates have also proven to be the material of choice for optical media applications such as optical discs, for example compact discs (CD) and digital versatile discs (DVD). Conventional polycarbonates are usually produced by (1) an interfacial polymerization, in which bisphenol A (BPA) is reacted directly with phosgene or (2) a melt polymerization process in which BPA is transesterified with a carbonic acid diester such as diphenyl carbonate (DPC). For many applications, there has been a need for materials possessing the fundamental characteristics of transparency and toughness inherent in BPA polycarbonate but possessing, in addition, certain improvements in physical properties relative those possessed by bisphenol A polycarbonate (BPA-PC), for example reduced birefringence for optical applications. For some applications improved chemical resistance relative to BPA polycarbonate is required, for example in certain medical and automotive applications. Copolycarbonates are materials frequently possessing the fundamental traits of BPA polycarbonate, transparency and toughness, but in certain instances also possessing improved performance characteristics for a given application relative to BPA polycarbonate.

One example of such a copolycarbonate comprises repeat units derived from resorcinol or hydroquinone in addition to repeat units derived from bisphenol A. The incorporation of resorcinol-derived and hydroquinone-derived repeat units into a BPA-polycarbonate confers excellent melt flow properties, molding properties, solvent and heat resistance, while maintaining the excellent mechanical properties and transparency inherent in bisphenol A polycarbonate. Such copolycarbonates can be prepared by interfacial polymerization, melt polymerization, or solid state polymerization. (U.S. Pat. No. 6,177,536). The present invention relates to an improved method to prepare these and related copolycarbonates using the melt polymerization method.

SUMMARY OF THE INVENTION

Applicants have determined that the formation of color in quinone-like copolycarbonates can be reduced by adding an antioxidant to the melt polymerization process. Thus, an embodiment of the present invention provides a method of producing a copolycarbonate with improved color wherein the method comprises the steps of,

i. preparing a molten reaction mixture comprising a first dihydroxy aromatic compound comprising monomer residue (a), a second dihydroxy aromatic compound comprising monomer residue (b), a carbonate source, and a polymerization catalyst,

-   -   wherein monomer residue (a) is a quinone structure or a         structure capable of forming a quinone structure upon oxidation,     -   wherein monomer residue (b) is a quinone structure or a         structure capable of forming a quinone structure upon oxidation         different from monomer residue (a), or is,

-   -   -   where B is

-   -   -    —O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a             C₆–C₂₀ cycloaliphatic radical; the groups R¹ and R² are             independently a hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀             cycloalkyl radical, or C₄–C₂₀ aryl radical; or R¹ and R²             together form a C₄–C₂₀ cycloaliphatic ring which is             optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀             aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a             combination thereof, R³ is a divalent hydrocarbylene group,             and R⁴ and R⁵ are independently a hydrogen atom, halogen             atom, nitro group, cyano group, C₁–C₂₀ alkyl radical C₄–C₂₀             cycloalkyl radical, or C₆–C₂₀ aryl radical and p and q are             both integers from 0 to 4,

ii. introducing an antioxidant such as a hydroxycarboxylic acid to the reaction mixture in an amount sufficient to result in a product copolycarbonate with improved color,

iii. introducing the reaction mixture to a series of process units, and

iv. allowing the reaction mixture to polymerize thereby forming copolycarbonate, wherein the copolycarbonate has improved color as compared to a copolycarbonate formed in a melt process without the introduction of antioxidant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an embodiment of a melt polymerization process of the current invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included therein. The present invention provides a method for improving the color of a copolycarbonate produced by melt polymerization wherein the copolycarbonate comprises monomer residues of dihydroxy aromatic compounds and diaryl carbonates. The method comprises the steps of;

-   -   i. preparing a molten reaction mixture comprising a first         dihydroxy aromatic compound comprising monomer residue (a), a         second dihydroxy aromatic compound comprising monomer residue         (b), a carbonate source, and a polymerization catalyst,         -   wherein monomer residue (a) is a quinone structure or a             structure capable of forming a quinone structure upon             oxidation,         -   wherein monomer residue (b) is a quinone structure or a             structure capable of forming a quinone structure upon             oxidation different from monomer residue (a), or is,

-   -   -   where B is

-   -   -    —O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a             C₆–C₂₀ cycloaliphatic radical; the groups R¹ and R² are             independently a hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀             cycloalkyl radical, or C₄–C₂₀ aryl radical; or R¹ and R²             together form a C₄–C₂₀ cycloaliphatic ring which is             optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀             aryl, C₅–C₂₁, aralkyl, C₅–C₂₀ cycloalkyl groups or a             combination thereof, R³ is a divalent hydrocarbylene group,             and R⁴ and R⁵ are independently a hydrogen atom, halogen             atom, nitro group, cyano group, C₁–C₂₀ alkyl radical C₄–C₂₀             cycloalkyl radical, or C₆–C₂₀ aryl radical and p and q are             both integers from 0 to 4,

    -   ii. introducing an antioxidant such as a hydroxycarboxylic acid         to the reaction mixture in an amount sufficient to result in a         product copolycarbonate with improved color,

    -   iii. introducing the reaction mixture to a series of process         units; and

    -   iv. allowing the reaction mixture to polymerize thereby forming         copolycarbonate, wherein the copolycarbonate has improved color         as compared to a copolycarbonate formed in a melt process         without the introduction of antioxidant.

In the specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:

The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

“Copolycarbonate” refers to polycarbonates incorporating repeat units derived from at least two dihydroxy aromatic compounds and includes copolyestercarbonates, for example a polycarbonate comprising repeat units derived from resorcinol, bisphenol A, and dodecandioic acid. Nothing in the description and claims of this application should be taken as limiting the copolycarbonate to only two dihydroxy aromatic residues unless the context is expressly limiting. Thus, the application encompasses copolycarbonates with residues of 2, 3, 4, or more types of dihydroxy aromatics.

“BPA” is herein defined as bisphenol A or 2,2-bis(4-hydroxyphenyl)propane.

“Substantial polymerization” is where the average molecular weight (M_(w)) of the copolycarbonate is less than 5,000 (PS standards).

“Melt polycarbonate” refers to a polycarbonate made by the transesterification of a diarylcarbonate with a dihydroxy aromatic compound.

“Catalyst system” as used herein refers to a catalyst or catalysts that catalyze the transesterification of a dihydroxy aromatic compound with a diarylcarbonate in the preparation of melt polycarbonate.

“Catalytically effective amount” refers to an amount of a catalyst at which catalytic performance is exhibited.

“Monomer mix tank” refers to the area of the process wherein the reaction mixture is prepared. The word tank does not limit the invention to the mixing of monomers within a single vessel. The mixing may occur in a series of tanks or by any other means to prepare a mixture.

“Process units” refers to the area within the system wherein the monomers react and where copolycarbonate weight is built. This may occur within, among other places, extruders, equilibration vessels, continuously stirred tank reactors, batch reactors, packed bed reactors or heat exchangers.

“Plaque Yellowness Index” refers to a measurement of color of a sample of copolycarbonate using a UV spectrophotometer converted to a 1 mm thick sample value. It is preferable that the copolycarbonate made by the method of the present invention have a plaque yellowness index value of between 0.4 and 8.0, more preferably between 0.04 and 5.0 and still more preferably between 0.04 and 3.0. The plaque YI of the resulting copolycarbonate is affected by the initial quality of the quinone type structure.

“Solution Yellowness Index” refers to the yellowness of the reaction mixture prior to substantial polymerization. Data can be measured with a UV/VIS spectrophotometer on a 10% Copolymer solution in MECl₂. The transmission can be measured on 3 wavelengths (445 NM, 555 NM, and 600 NM) against a MeCl₂ blank. With the following calculation the sol YI can be calculated; (Sol YI=(% T600−% T445)/% T555*100%).

“Dihydroxy aromatic compound(s)” means an aromatic compound which comprises two hydroxy groups on one or more aromatic rings, for example a bisphenol such as bisphenol A or a dihydroxy benzene such as resorcinol.

Numerical values in the specification and claims of this application, particularly as they relate to polymer compositions, reflect average values for a composition that may contain individual polymers of different characteristics. Furthermore, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of the measurement technique used in the present application to determine the value.

The present invention provides a method for preparing a copolycarbonate. An embodiment of the method comprises contacting under melt polymerization conditions a first dihydroxy aromatic compound containing the precursor of monomer residue (a), and at least one second dihydroxy aromatic compound containing the precursor of monomer residue (b), with at least one diarylcarbonate containing the precursor of monomer residue (c), an antioxidant and at least one melt polymerization catalyst.

The First Dihydroxy Aromatic Compound:

The first dihydroxy aromatic compound comprises monomer residue (a). It can be any quinone structure or structure capable of forming a quinone structure upon oxidation. Suitable types of these dihydroxy aromatic compounds may be selected from the group consisting of dihydroxy benzenes having structure I

where each R¹⁰ is independently at each occurrence a hydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkyl radical, C₄–C₂₀ aryl radical, and n is an integer from 0 to 4.

Non-limiting examples of dihydroxy benzenes having structure I are resorcinol; hydroquinone; 4-methylresorcinol; 5-methylresorcinol; 2-methylhydroquinone; 2-ethylhydroquinone; 2,5-dimethylhydroquinone; 2,6-dimethylhydroquinone; catechol; 3-methylcatechol; 4-methylcatechol; butylhydroquinone; and mixtures thereof.

The Second Dihydroxy Aromatic Compound:

The second dihydroxy aromatic compound forms the precursor of monomer residue (b) such that the polymer formed is a copolycarbonate. It can be any quinone structure or structure capable of forming a quinone structure upon oxidation different from monomer residue (a) such that the polymer formed is a copolycarbonate. Suitable types of these dihydroxy aromatic compounds again may be selected from the group consisting of dihydroxy benzenes having structure I

where each R¹⁰ is as defined as above and non non-limiting examples of such are as defined above.

Alternatively the second dihydroxy aromatic compound may be a bisphenol having structure II

where B is,

—O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀ cycloaliphatic radical; the groups R¹ and R² are independently a hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphatic ring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁, aralkyl, C₁–C₂₀ cycloalkyl groups or a combination thereof, R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl radical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and q are both integers from 0 to 4.

Bisphenols having structure II are illustrated by 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); 2,2-bis(3-chloro-4-hydroxyphenyl)propane; 2,2-bis(3-bromo-4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-methylphenyl)propane; 2,2-bis(4-hydroxy-3-isopropylphenyl)propane; 2,2-bis(3-t-butyl-4-hydroxyphenyl)propane; 2,2-bis(3-phenyl-4-hydroxyphenyl)propane; 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane; 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane; 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; 2,2-bis(3-chloro-4-hydroxy-5-methylphenyl)propane; 2,2-bis(3-bromo-4-hydroxy-5-methylphenyl)propane; 2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane; 2,2-bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane; 2,2-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)propane; 2,2-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)propane; 2,2-bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane; 2,2-bis(3-bromo-5-phenyl-4-hydroxyphenyl)propane; 2,2-bis(3,5-disopropyl-4-hydroxyphenyl)propane; 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane; 2,2-bis(3,5-diphenyl-4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane; 2,2-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane; 2,2-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)propane; 2,2-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)propane; 2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane; 1,1-bis(4-hydroxyphenyl)cyclohexane; 1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane; 1,1-bis(3-bromo-4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-bis(4-hydroxy-3-isopropylphenyl)cyclohexane; 1,1-bis(3-t-butyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane; 1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane; 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)cyclohexane; 1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)cyclohexane; 1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)cyclohexane; 1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)cyclohexane; 1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)cyclohexane; 1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3-chloro-5-phenyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(3,5-diphenyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)cyclohexane; 1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)cyclohexane; 1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)cyclohexane; 1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-bromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 4,4′dihydroxy-1,1-biphenyl; 4,4′-dihydroxy-3,3′-dimethyl-1,1-biphenyl; 4,4′-dihydroxy-3,3′-dioctyl-1,1-biphenyl; 4,4′-dihydroxydiphenylether; 4,4′-dihydroxydiphenylthioether; 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; 1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene; 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; and 1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene. In many applications due to its relatively high reactivity, thermal stability, and low cost, bisphenol A (BPA) is frequently preferred.

The Carbonate Source:

In the production of copolymerized polycarbonates in accordance with the present invention, the compounds which react with the dihydroxy compounds to form carbonate linkages (the carbonate source) may be carbonate diesters, carbonyl halides, etc. Specific examples include: diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, m-cresyl carbonate dinaphthyl carbonate, bis(diphenyl)carbonate, diethyl carbonate, dimethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, and other carbonate diesters, phosgene, and other carbonyl halides. Of the various compounds of this type, diphenyl carbonate is often preferred.

The carbonate can be also be derived from an activated dicarbonate or a mixture of an activated carbonate with diphenyl carbonate. A preferred activated carbonate of the present invention is an activated diarylcarbonate such as bismethylsalicylcarbonate (BMSC). However, as used herein the term “activated carbonate” is defined as a diarylcarbonate which is more reactive than diphenylcarbonate toward transesterification reactions. Such activated carbonates are of the general formula:

wherein Ar is a substituted aromatic radical having 6 to 30 carbon atoms. The preferred activated carbonates have the more specific general formula:

wherein Q and Q′ are each independently activating groups. A and A′ are each independently aromatic rings which can be the same or different depending on the number and location of their substituent groups, and n or n′ are whole numbers of zero up to a maximum equivalent to the number of replaceable hydrogen groups substituted on the aromatic rings A and A′, wherein A+A′ is greater than or equal to 1. R and R′ are each independently substituent groups such as alkyl, substituted alkyl, cycloalkyl, alkoxy, aryl, alkylaryl, cyano, nitro, halogen, and carboalkoxy. The number of R groups is a whole number and can be 0 up to a maximum equivalent to the number of replaceable hydrogen groups on the aromatic rings A minus the number n. The number of R′ groups is a whole number and can be 0 up to a maximum equivalent to the number of replaceable hydrogen groups on the aromatic rings A minus the number n′. The number, type, and location of the R and R′ substituents on the aromatic ring are not limited unless they deactivate the carbonate and lead to a carbonate which is less reactive than diphenylcarbonate.

Non-limiting examples of activating groups Q and Q′ are: alkoxycarbonyl groups, halogens, nitro groups, amide groups, sulfone groups, sulfoxide groups, or imine groups with structures indicated below:

Specific and non-limiting examples of activated carbonates include bis(o-methoxycarbonylphenyl)carbonate, bis(o-chlorophenyl)carbonate, bis(o-nitrophenyl)carbonate, bis(o-acetylphenyl)carbonate, bis(o-phenylketonephenyl)carbonate, bis(o-formylphenyl)carbonate. Unsymmetrical combinations of these structures, where the substitution number and type on A and A′ are different, are also possible to employ in the current invention. A preferred structure for an activated carbonate is an ester-substituted diarylcarbonate having the structure:

wherein R¹ is independently at each occurrence a C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aromatic radical; R² is independently at each occurrence a halogen atom, cyano group, nitro group, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, C₄–C₂₀ aromatic radical, C₁–C₂₀ alkoxy radical, C₄–C₂₀ cycloalkoxy radical, C₄–C₂₀ aryloxy radical, C₁–C₂₀ alkylthio radical, C₄–C₂₀ cycloalkylthio radical, C₄–C₂₀ arylthio radical, C₁–C₂₀ alkylsulfinyl radical, C₄–C₂₀ cycloalkylsulfonyl radical, C₄–C₂₀ arylsulfinyl radical, C₁–C₂₀ alkylsulfonyl radical, C₄–C₂₀ cycloalkylsulfonyl radical, C₄–C₂₀ arylsulfonyl radical, C₁–C₂₀ alkoxycarbonyl radical, C₄–C₂₀ cycloalkoxycarbonyl radical, C₄–C₂₀ aryloxycarbonyl radical, C₂–C₆₀ alkylamino radical, C₆–C₆₀ cycloalkylamino radical, C₅–C₆₀ arylamino radical, C₁–C₄₀ alkylaminocarbonyl radical, C₄–C₄₀ cycloalkylaminocarbonyl radical, C₄–C₄₀ arylaminocarbonyl radical, or C₁–C₂₀ acylamino radical; and b is independently at each occurrence an integer 0–4. At least one of the substituents CO₂R¹ is preferably attached in an ortho position relative to the carbonate group.

Examples of preferred ester-substituted diarylcarbonates include but are not limited to bis(methylsalicyl)carbonate (CAS Registry No. 82091-12-1), bis(ethyl salicyl)carbonate, bis(propyl salicyl) carbonate, bis(butylsalicyl) carbonate, bis(benzyl salicyl)carbonate, bis(methyl 4-chlorosalicyl)carbonate and the like. Typically bis(methylsalicyl)carbonate is preferred for use in melt polycarbonate synthesis due to its lower molecular weight and higher vapor pressure.

Some non-limiting examples of non-activating groups which, when present in an ortho position relative to the carbonate group, would not be expected to result in activated carbonates are alkyl, cycolalkyl or cyano groups. Some specific and non-limiting examples of non-activated carbonates are bis(o-methylphenyl)carbonate, bis(p-cumylphenyl)carbonate, bis(p-(1,1,3,3-tetramethyl)butylphenyl)carbonate and bis(o-cyanophenyl)carbonate. Unsymmetrical combinations of these structures are also expected to result in non-activated carbonates.

Unsymmetrical diarylcarbonates wherein one aryl group is activated and one aryl is unactivated or de-activated would also be useful in this invention if the activating group renders the diaryl carbonate still more reactive than diphenyl carbonate.

The carbonate may also be derived from dicarboxylic acids, dicarboxylic acid esters, or dicarboxylic acid halides. Such constituent repeating units are typically polyester-polycarbonate units. Non-limiting examples of dicarboxylic acids include terephthalic acid, isophthalic acid, sebacic acid, decanedioic acid, dodecanedioic acid, etc. Non-limiting examples of dicarboxylic acid esters include diphenyl sebacate, diphenyl terephthalate, diphenyl isophthalate, diphenyl decanedioate, diphenyl dodecanedioate, etc. Non-limiting examples of dicarboxylic acid halides include terephthaloyl chloride, isophthaloyl chloride, sebacoyl chloride, decanedioyl chloride, dodecanedioyl chloride, etc. Such polyester-polycarbonate units may be present in proportions of up to 50 mole %, preferably not more than 30 mole %, in copolymerized polycarbonates in accordance with the present invention.

The Catalyst:

The method of the invention also comprises the step of introducing a catalyst to the reaction mixture to initiate a polymerization reaction. The catalyst may be introduced continuously, or may be introduced batchwise and may occur before, during or after the introduction of the precursors of monomer residues (a) or (b), or the carbonate.

The catalyst used in the method of the present invention is a base, and preferably comprises at least one source of alkaline earth ions or alkali metal ions, and/or at least one quaternary ammonium compound, a quaternary phosphonium compound or a mixture thereof. The source of alkaline earth ions or alkali metal ions being used in an amount such that the amount of alkaline earth or alkali metal ions present in the reaction mixture is in a range between 10⁻⁵ and 10⁻⁸ moles alkaline earth or alkali metal ion per mole of dihydroxy aromatic compound employed.

The quaternary ammonium compound is selected from the group of organic ammonium compounds having structure III,

wherein R²⁰–R²³ are independently a C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or a C₄–C₂₀ aryl radical; and X⁻ is an organic or inorganic anion. In one embodiment of the present invention anion X⁻ is selected from the group consisting of hydroxide, halide, carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate.

Non-limiting examples of suitable organic ammonium compounds comprising structure III are tetramethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, tetramethyl ammonium acetate, tetramethyl ammonium formate and tetrabutyl ammonium acetate. Tetramethyl ammonium hydroxide is often preferred.

The quaternary phosphonium compound is selected from the group of organic phosphonium compounds having structure IV,

wherein R²⁴–R²⁷ are independently a C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or a C₄–C₂₀ aryl radical; and X⁻ is an organic or inorganic anion. In one embodiment of the present invention anion X⁻ is an anion selected from the group consisting of hydroxide, halide, carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate. Suitable organic phosphonium compounds comprising structure TV are illustrated by tetramethyl phosphonium hydroxide, tetramethyl phosphonium acetate, tetramethyl phosphonium formate, tetrabutyl phosphonium hydroxide, and tetrabutyl phosphonium acetate (TBPA). TBPA is often preferred.

Where X⁻ is a polyvalent anion such as carbonate or sulfate it is understood that the positive and negative charges in structures III and IV are properly balanced. For example, where R²⁰–R²³ in structure III are each methyl groups and X⁻ is carbonate, it is understood that X⁻ represents ½ (CO₃ ⁻²).

Suitable sources of alkaline earth ions include alkaline earth hydroxides such as magnesium hydroxide and calcium hydroxide. Suitable sources of alkali metal ions include the alkali metal hydroxides illustrated by lithium hydroxide, sodium hydroxide and potassium hydroxide. Other sources of alkaline earth and alkali metal ions include salts of carboxylic acids, such as sodium acetate and derivatives of ethylene diamine tetraacetic acid (EDTA) such as EDTA tetrasodium salt, and EDTA magnesium disodium salt. Sodium hydroxide is often preferred.

In order to achieve the formation of copolycarbonate using the method of the present invention an effective amount of catalyst must be employed. The amount of catalyst employed is typically based upon the total number of moles of first dihydroxy aromatic compound and second dihydroxy aromatic compound employed in the polymerization reaction. When referring to the ratio of catalyst, for example phosphonium salt IV, to all dihydroxy aromatic compounds employed in the polymerization reaction, it is convenient to refer to moles of phosphonium salt per mole of the first and second dihydroxy aromatic compounds combined, meaning the number of moles of phosphonium salt divided by the sum of the moles of each individual dihydroxy aromatic compound present in the reaction mixture. The amount of organic ammonium or phosphonium salts III or IV employed typically will be in a range between 1×10⁻² and 1×10⁻⁵, preferably between 1×10⁻³ and 1×10⁻⁴ moles per mole of the first and second dihydroxy aromatic compounds combined. The inorganic metal hydroxide catalyst typically will be used in an amount corresponding to between 1×10⁻⁴ and 1×10⁻⁸, preferably 1×10⁻⁴ and 1×10⁻⁷ moles of metal hydroxide per mole of the first and second dihydroxy aromatic compounds combined.

The Antioxidant:

Several types of antioxidants may be used in accordance with the present invention. Exemplary of antioxidants that may be used in accordance with the present invention are hydroxycarboxylic acids, benzofuranones, phenolic antioxidants including sterically hindered phenols, hydroxylamines including dialkylhydroxylamines, functionalized aliphatic hydroxylamines, or substituted dibenzylhydroxylamine.

Non-limiting examples of hydroxycarboxylic acids that may be used include tartaric acid, maleic acid, lactic acid, tartronic acid and esters of these acids. It is yet another aspect of the present invention that the salts of the aforementioned acids be used.

An effective amount of antioxidant should be introduced to the reaction mixture in order to ensure a copolycarbonate product with improved color. An excessive amount may have the effect of degrading the catalyst used in the reaction. Thus in certain embodiments, an effective amount of hydroxycarboxylic acid is less than 10 ppm, more preferably less than 5 ppm, and still more preferably less than 1 ppm based on the weight of the precursor of monomer residue (a) in the molten reaction mixture.

The Melt Process:

The term “contacting under melt polymerization conditions” will be understood to mean those conditions necessary to effect reaction between the diarylcarbonate and the dihydroxy aromatic compounds employed according to the method of the present invention. The reaction temperature is typically in the range between 150° C. and 350° C., more preferably between 180° C. and 310° C. The pressure may be at atmospheric pressure, supra atmospheric pressure, or a range of pressures, for example from 2 atmospheres to 15 torr in the initial stages of the polymerization reaction, and at a reduced pressure at later stages, for example in a range between 15 torr and 0.1 torr. The reaction time is generally in a range between 0.1 hours and 10 hours, preferably between 0.1 and 5 hours.

FIG. 1 illustrates a melt process according to an embodiment of the present invention. The first stage of the process is to mix the first and second dihydroxy aromatic compounds, comprising the precursors of monomer residues (a) and (b), with the carbonate compound, thereby forming a reaction mixture. An antioxidant is introduced to the reaction mixture either during its preparation or after the mixture has been prepared. The reaction mixture is then fed to a series of process equipment wherein a copolymerization reaction takes place and molecular weight of the resulting copolycarbonate is increased.

In one embodiment of the present invention, at least one first dihydroxy aromatic compound comprising the precursor of monomer residue (a) and at least one second dihydroxy aromatic compound comprising the precursor of monomer residue (b) are employed in amounts such that the molar ratio of the first dihydroxy aromatic compound to the second dihydroxy aromatic compound is in a range between 0.01 and 99.00. Where the second dihydroxy aromatic compound comprises two or more compounds, for example a mixture of resorcinol and hydroquinone, and the first dihydroxy compound is a single compound, for example BPA, the molar ratio of the first dihydroxy aromatic compound to the second dihydroxy aromatic compound is expressed as the sum of the number of moles of resorcinol and hydroquinone used divided by the number of moles of BPA used. Similarly, where the second dihydroxy aromatic compound comprises but a single compound, for example resorcinol, and the first dihydroxy aromatic compound comprises a mixture of compounds, for example, BPA and BPZ (1,1-bis(4-hydroxyphenyl)cyclohexane), the molar ratio of the second dihydroxy aromatic compound to the first dihydroxy aromatic compound is expressed as the number of moles of resorcinol used divided by the sum of the number of moles of BPA and BPZ used. As mentioned, in one embodiment the molar ratio of the second dihydroxy aromatic compound to the first dihydroxy aromatic compound is in a range between 0.01 and 99. In an alternate embodiment the molar ratio of the second dihydroxy aromatic compound to the first dihydroxy aromatic compound is in a range between 0.05 and 0.7. A copolycarbonate prepared according to the method of the present invention using resorcinol as the second dihydroxy aromatic compound and BPA as the first dihydroxy aromatic compound in which the molar ratio of resorcinol to BPA was 0.7 could contain as much as 41 mole percent resorcinol derived repeat units if no loss occurred during the polymerization reaction.

Typically, the method of the present invention is carried out such that the amount of diarylcarbonate employed corresponds to a molar ratio of diarylcarbonate to all dihydroxy aromatic compounds, i.e. the first and/or second dihydroxy aromatic compounds, initially present in the reaction mixture, the molar ratio being in a range between 0.90 and 1.20, preferably between 1.01 and 1.10.

The method of the present invention further comprises the step of introducing an antioxidant to the reaction mixture. The introduction of the antioxidant may take place at any one or a combination of places within the polymerization process. As illustrated in FIG. 1, an embodiment of the melt process of the present invention includes several basic stages. The first stage is to mix the precursors of monomer residues (a), monomer residues (b), a carbonate source and a polymerization catalyst into a reaction mixture. The reaction mixture is then fed to a series of process equipment wherein polymerization reactions occur thereby building polymer weight.

The antioxidant may be introduced to the reaction mixture prior to or during the melting of monomer residues (a), monomer residues (b), or the carbonate source may be introduced in a melter or a feed line to a melter. Further, the antioxidant may be introduced to the reaction mixture after melting monomer residues (a), monomer residues (b), and the carbonate source. If so, it may be introduced to the molten reaction mixture in a melter, a feed line to a monomer mix tank, the monomer mix tank, a feed line from the monomer mix tank to a first process unit, the first process unit, a feed line to a second process unit, the second process unit, a feed line to a third process unit, the third process unit, or combinations thereof. In order to prevent further undesirable oxidation reactions with the melt polymerization catalyst it is often preferred that the introduction of the antioxidant occur prior to the introduction of the polymerization catalyst.

Optional Catalyst Introduction Strategy

U.S. patent application Ser. No. 10/768,575, herein incorporated by reference, discloses and claims a method of reducing the color generated during the production of polycarbonates. In some embodiments, in addition to the introduction of an antioxidant, the method of the present invention includes the steps of selecting a catalyst introduction strategy to reduce color formation and introducing the catalysts to the reaction mixture in accordance with the selected strategy. As noted the catalyst introduction strategy incorporates the introduction of an organic catalyst and an inorganic catalyst.

FIG. 1 shows a melt polymerization processes of the type that may be employed with the current invention. Precursors of monomer residues (a) and (b), and a carbonate source are introduced to a monomer mix tank where they are mixed thereby forming a reaction mixture. The reaction mixture is then sent to a series of process units wherein polymerization reactions occur and copolymer weight increases. The polymerization catalysts are added to the reaction mixture per a selected strategy. The catalyst introduction strategies of the present invention include several potential introduction points of organic and/or inorganic catalysts.

The polymerization catalysts introduction may occur in at least three schemes. The first scheme is to introduce the polymerization catalysts to the reaction mixture after monomer (a), monomer (b) and the carbonate source have been melted and prior to substantial polymerization of the monomers. The second strategy is to introduce the polymerization catalysts to the reaction mixture or precursors of one or more of the monomer residues prior to melting with the proviso that residence time of the process from the start of melting until substantial polymerization has occurred is less than 4 hours. The third strategy is to combine the first two strategies wherein the organic catalyst is introduced to the reaction mixture prior to melting and the inorganic catalyst is introduced after melting. The purpose of selecting the strategy is so that the polymerization catalysts have minimal contact with the reaction mixture so as to prevent an undesirable oxidation reaction which produces an undesirable color formation within the resulting copolycarbonate.

Strategy 1:

The method of the present invention comprises the strategy of introducing the polymerization catalysts to the reaction mixture after monomer residues (a), monomer residues (b), and carbonate source are melted and prior to substantial polymerization. The organic and inorganic catalysts may be introduced to the reaction mixture either together or at separate points.

The introduction of the organic catalyst may occur in a monomer mix tank, or in a feed line to a first process unit. The organic catalyst may be introduced to the reaction mixture as it is prepared if melting is performed prior to combination of the components, and may be introduced with the monomer residues or the carbonate source either in the same feed lines or in a separate feed line.

The introduction of the inorganic catalyst typically occurs at the same time or after the introduction of the organic catalyst. If the introduction occurs at the same time, the catalysts may be introduced within the same feed or in separate feeds at any of the aforementioned points where the organic catalyst may be introduced. It is preferred, however, that the introduction of the catalyst solution to the molten reaction occur subsequent to the introduction of the precursor of monomer residue (a).

If the introduction of the inorganic catalyst occurs a different point than the introduction of the organic catalyst then the organic catalyst is desirably introduced to the molten reaction mixture prior to a first process unit while the inorganic catalyst is introduced to the molten reaction mixture at any one of various points prior to substantial polymerization of the molten reaction mixture. The inorganic catalyst may be introduced in the feed line from the monomer mix tank to a first process unit, or to the molten reaction mixture in the first process unit, or to the molten reaction mixture in a feed line to a second process unit, or to the molten reaction mixture in the second process unit, or to the molten reaction mixture in a feed line to a third process unit, or to the third process unit itself.

Strategy 2:

The method of the present invention comprises the strategy of introducing a polymerization catalyst to the reaction mixture prior to melting monomer residues (a), monomer residues (b), and carbonate source with the proviso that residence time of the process from the start of melting until substantial polymerization has occurred is less than 4 hours, more preferably 30 minutes or less, and most preferably 15 minutes or less.

The organic and inorganic catalysts may be introduced to the reaction mixture either together or at separate points. The inorganic and organic catalysts may be introduced to a monomer mix tank or a melter together with monomer residues (a), together with monomer residues (b), together with the carbonate source, in a separate feed or combinations thereof.

Strategy 3:

The method of the present invention comprises the strategy of introducing a polymerization catalyst to the reaction mixture wherein the organic catalyst is introduced to a monomer mix tank or a melter together with monomer residue (a), together with monomer residue (b), together with the carbonate source, in a separate feed or combinations thereof. The inorganic catalyst is then introduced to the molten reaction mixture, prior to substantial polymerization, within a monomer mix tank, a feed line from a monomer mix tank to a first process unit, the first process unit, a feed line to a second process unit, the second process unit, a feed line to a third process unit, the third process unit, or combinations thereof.

An embodiment of the present invention further comprises the step of introducing a dihydric phenol or other monomer to the molten reaction mixture within the series of process units through late monomer addition. This addition of dihydric phenol may occur within the first, second, third or subsequent process units or the feed lines there between. It is preferable that the antioxidant is introduced to the reaction mixture prior to the late monomer addition. However, it is possible to add the acid with the monomer of the late monomer addition.

The method of the present invention may be employed to provide high molecular weight copolycarbonates. High molecular weight copolycarbonates are defined as copolycarbonates having a weight average molecular weight, M_(w), greater than 15,000 (PS standards). The method of the present invention may also be employed to provide oligomeric copolycarbonates. Oligomeric copolycarbonates are defined as copolycarbonates as having weight average molecular weight, M_(w), less than 15,000 (PS standards).

The invention also provides a method for making a molded article and a molded article formed from copolycarbonate with improved color prepared by the method including the steps of: preparing a molten reaction mixture comprising a first dihydroxy aromatic compound comprising monomer residue (a), a second dihydroxy aromatic compound comprising monomer residue (b), a carbonate source, and a polymerization catalyst; introducing an antioxidant such as a hydroxycarboxylic acid to the reaction mixture in an amount sufficient to result in a product copolycarbonate with improved color; introducing the reaction mixture to a series of process units; allowing the reaction mixture to polymerize thereby forming copolycarbonate, wherein the copolycarbonate has improved color as compared to a copolycarbonate formed in a melt process without the introduction of antioxidant; and forming a molded article from the copolycarbonate. The molded articles may be molded by inter alia the processes of injection molding, blow molding, extrusion or coextrusion.

Blends of copolymers are typical in industry. Thus the copolycarbonates prepared using the method of the present invention may be blended with other polymeric materials, for example, other polycarbonates, polyestercarbonates, polyesters and olefin polymers such as ABS. Further, the copolycarbonates prepared using the method of the present invention may be blended with conventional additives such as heat stabilizers, mold release agents, and UV stabilizers. These blends may be molded into various articles such as optical disks, optical lenses, automobile lamp components and the like. Thus, it is an aspect of the present invention to provide molded articles comprising the blends of copolycarbonate and/or the copolycarbonate produced by the method of the present invention.

EXAMPLES

Having described the invention in detail, the following examples are provided. The examples should not be considered as limiting the scope of the invention, but merely as illustrative and representative thereof. The following measurements were made in these examples:

-   a.) Molecular weight: M_(w) and M_(n) were measured by GPC analysis     of 1 mg/ml polymer solutions in methylene chloride versus     polystyrene (PS) standards. -   b.) Solution Yellowness Index (YI) data was measured with a UV/VIS     spectrophotometer on a 10% Copolymer solution in MeCl₂. The     transmission was measured on 3 wavelengths (445 nm, 555 nm, and 600     nm) against a MeCl₂ blank. With the following calculation the sol YI     was calculated;     Sol YI=(% T600−% T445)/% T555*100% -   c.) Small Scale Melt Polymerization reactions were carried out with     BPA and additional monomer(s). See Examples 1 through 6 and Table 2.     The total amount of DPC (moles) equaled 1.08*(BPA+co-monomer/(total     moles bisphenol)). The amount of DPC was held constant at 25 g in     each reaction. As catalysts, TMAH/(BPA+co-monomer)=2.5×10⁻⁴     (mole/mole) and NaOH (BPA+co-monomer)=1.5×10⁻⁶ (mole/mole) were     added as an aqueous solution (100 μl). Reactions were carried out by     mixing aromatic dihydroxy compounds with DPC. After Nitrogen purging     of the reactor system, polymerizations were carried out according to     the reaction scheme illustrated in Table 1.

TABLE 1 Reaction scheme for small scale melt polymerizations. Reaction Stage Time (min) Temp (° C.) P (mbar) 1 480 180 atm 2 60 230 170 3 30 270  20 4 30 300 0.5–1.5

At the end of the reaction, the reactor was brought back to atmospheric pressure with a gentle nitrogen flow, and the polymer was harvested. The melting time of 480 minutes was chosen to simulate plant conditions.

Example 1

In example 1, a batch reactor tube was charged under nitrogen with 19.73 g of BPA, 2.38 g of resorcinol, 25.00 g of DPC, and 100 (μl) of an aqueous solution of TMAH and NaOH (2.5×10⁻⁴ and 1.5×10⁻⁶ moles catalyst/mole aromatic dihydroxy compound). Before the reaction, 1 ppm (relative to the amount of resorcinol) of tartaric acid was added to the reaction mixture as an aqueous solution of 100 (μl).

Example 2 (Comparative)

Example 1 was repeated without the addition of an antioxidant.

Example 3 (Comparative)

Example 2 was repeated except that the batch reactor tube was charged under nitrogen with 24.76 g of BPA, 25.00 g of DPC, and no resorcinol.

Example 4

Example 1 was repeated with 9 ppm (relative to the amount of resorcinol) of tartaric acid.

Example 5

Example 1 was repeated with (relative to the amount of resorcinol) of 0.5 ppm tartaric acid.

Example 6

Example 1 was repeated with 1 ppm (relative to the amount of resorcinol) of tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane, CAS Reg. Number [6683-19-8].

TABLE 2 Experimental Results Example Mw (kg/mol) YI (Solution) 1 38.0 2.9  2* 56.0 8.2  3* 38.1 1.2 4 33.3 2.4 5 34.3 2.9 6 34.9 2.4 *= Comparative 

1. A method of producing a copolycarbonate with improved color wherein the method comprises the steps of, i. preparing a molten reaction mixture comprising a first dihydroxy aromatic compound comprising monomer residue (a), a second dihydroxy aromatic compound comprising monomer residue (b), a carbonate source, and a polymerization catalyst, wherein monomer residue (a) is a quinone structure or a structure capable of forming a quinone structure upon oxidation, wherein monomer residue (b) is a quinone structure or a structure capable of forming a quinone structure upon oxidation different from monomer residue (a), or is,

where B is

—O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀ cycloaliphatic radical; the groups R¹ and R² are independently a hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphatic ring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a combination thereof, R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl radical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and q are both integers from 0 to 4, ii. introducing an antioxidant selected from the group consisting of hydroxycarboxylic acids, benzofuranones, phenolic antioxidants, hydroxylamines, functionalized aliphatic hydroxylamines, and substituted dibenzylhydroxylamine to the reaction mixture in an amount sufficient to result in a product copolycarbonate with improved color, iii. introducing the reaction mixture to a series of process units, and iv. allowing the reaction mixture to polymerize thereby forming copolycarbonate, wherein the copolycarbonate has improved color as compared to a copolycarbonate formed in a melt process without the introduction of antioxidant.
 2. The method of claim 1, wherein the antioxidant is introduced to the reaction mixture prior to melting, during melting, or after melting monomer residues (a), monomer residues (b), the carbonate source or combinations thereof.
 3. The method of claim 2, wherein the antioxidant is introduced to the reaction mixture prior to melting monomer residues (a), monomer residues (b), or the carbonate source wherein the introduction of the antioxidant occurs in a melter or a feed line to a melter.
 4. The method of claim 2, wherein the antioxidant is introduced to the reaction mixture after melting monomer residues (a), monomer residues (b), and the carbonate source wherein the introduction of the antioxidant to the molten reaction mixture occurs in a melter, a feed line to a monomer mix tank, the monomer mix tank, a feed line from the monomer mix tank to a first process unit, the first process unit, a feed line to a second process unit, the second process unit, a feed line to a third process unit, the third process unit, or combinations thereof.
 5. The method of claim 2, wherein the wherein the antioxidant is introduced to the reaction mixture during the melting of monomer residues (a), monomer residues (b), or the carbonate source wherein the introduction of the antioxidant occurs in a melter or a feed line to a melter.
 6. The method of claim 2, wherein the antioxidant is introduced in an amount of less than 10 ppm based on the weight of the precursor of monomer residue (a) in the reaction mixture.
 7. The method of claim 2, wherein the antioxidant is introduced in an amount of less than 5 ppm based on the weight of the precursor of monomer residue (a) in the reaction mixture.
 8. The method of claim 7, wherein the antioxidant is introduced in an amount of less than 1 ppm based on the weight of the precursor of monomer residue (a) in the molten reaction mixture.
 9. The method of claim 2, wherein the antioxidant is a hydroxycarboxylic acid and is selected from the group consisting of tartaric acid, maleic acid, lactic acid, tartronic acid and esters of these acids.
 10. The method of claim 2, wherein the antioxidant is a hydroxycarboxylic acid is selected from the group consisting of the salts of tartaric acid, salts of maleic acid, salts of lactic acid, and salts of tartronic acid.
 11. The method of claim 2, wherein the antioxidant is introduced to the reaction mixture prior to the introduction of the polymerization catalyst.
 12. The method of claim 1, wherein monomer residue (a) has the structure,

where each R¹⁰ is independently at each occurrence a hydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkyl radical, C₄–C₂₀ aryl radical, and n is an integer from 0 to
 4. 13. The method of claim 12, wherein monomer residue (a) is catechol, resorcinol, hydroquinone, butyl hydroquinone, methyl hydroquinone or any combination thereof.
 14. The method of claim 12, wherein the antioxidant is introduced to the reaction mixture prior to melting, during melting, or after melting monomer residues (a), monomer residues (b), the carbonate source or combinations thereof.
 15. The method of claim 12, wherein the antioxidant is introduced to the reaction mixture prior to melting monomer residues (a), monomer residues (b), or the carbonate source wherein the introduction of the antioxidant occurs in a melter or a feed line to a melter.
 16. The method of claim 12, wherein the antioxidant is introduced to the reaction mixture after melting monomer residues (a), monomer residues (b), and the carbonate source wherein the introduction of the antioxidant to the molten reaction mixture occurs in a melter, a feed line to a monomer mix tank, the monomer mix tank, a feed line from the monomer mix tank to a first process unit, the first process unit, a feed line to a second process unit, the second process unit, a feed line to a third process unit, the third process unit, or combinations thereof.
 17. The method of claim 12, wherein the wherein the antioxidant is introduced to the reaction mixture during the melting of monomer residues (a), monomer residues (b), or the carbonate source wherein the introduction of the antioxidant occurs in a melter or a feed line to a melter.
 18. The method of claim 12, wherein the antioxidant is introduced in an amount of less than 10 ppm based on the weight of the precursor of monomer residue (a) in the reaction mixture.
 19. The method of claim 12, wherein the antioxidant is introduced in an amount of less than 5 ppm based on the weight of the precursor of monomer residue (a) in the reaction mixture.
 20. The method of claim 19, wherein the antioxidant is introduced in an amount of less than 1 ppm based on the weight of the precursor of monomer residue (a) in the molten reaction mixture.
 21. The method of claim 12, wherein the antioxidant is a hydroxycarboxylic acid and is selected from the group consisting of tartaric acid, maleic acid, lactic acid, tartronic acid and esters of these acids.
 22. The method of claim 12, wherein the antioxidant is a hydroxycarboxylic acid is selected from the group consisting of the salts of tartaric acid, salts of maleic acid, salts of lactic acid, and salts of tartronic acid.
 23. The method of claim 12, wherein the antioxidant is introduced to the reaction mixture prior to the introduction of the polymerization catalyst.
 24. The method of claim 1, wherein monomer residue (b) is BPA.
 25. The method of claim 24, wherein the antioxidant is introduced to the reaction mixture prior to melting, during melting, or after melting monomer residues (a), monomer residues (b), the carbonate source or combinations thereof.
 26. The method of claim 25, wherein the antioxidant is introduced to the reaction mixture prior to melting monomer residues (a), monomer residues (b), or the carbonate source wherein the introduction of the antioxidant occurs in a melter or a feed line to a melter.
 27. The method of claim 25, wherein the antioxidant is introduced to the reaction mixture after melting monomer residues (a), monomer residues (b), and the carbonate source wherein the introduction of the antioxidant to the molten reaction mixture occurs in a melter, a feed line to a monomer mix tank, the monomer mix tank, a feed line from the monomer mix tank to a first process unit, the first process unit, a feed line to a second process unit, the second process unit, a feed line to a third process unit, the third process unit, or combinations thereof.
 28. The method of claim 25, wherein the wherein the antioxidant is introduced to the reaction mixture during the melting of monomer residues (a), monomer residues (b), or the carbonate source wherein the introduction of the antioxidant occurs in a melter or a feed line to a melter.
 29. The method of claim 25, wherein the antioxidant is introduced in an amount of less than 10 ppm based on the weight of the precursor of monomer residue (a) in the reaction mixture.
 30. The method of claim 25, wherein the antioxidant is introduced in an amount of less than 5 ppm based on the weight of the precursor of monomer residue (a) in the reaction mixture.
 31. The method of claim 30, wherein the antioxidant is introduced in an amount of less than 1 ppm based on the weight of the precursor of monomer residue (a) in the molten reaction mixture.
 32. The method of claim 25, wherein the antioxidant is a hydroxycarboxylic acid and is selected from the group consisting of tartaric acid, maleic acid, lactic acid, tartronic acid and esters of these acids.
 33. The method of claim 25, wherein the antioxidant is a hydroxycarboxylic acid is selected from the group consisting of the salts of tartaric acid, salts of maleic acid, salts of lactic acid, and salts of tartronic acid.
 34. The method of claim 25, wherein the antioxidant is introduced to the reaction mixture prior to the introduction of the polymerization catalyst.
 35. The method of claim 1, wherein the carbonate source is diphenyl carbonate.
 36. The method of claim 1, wherein the carbonate source is an activated carbonate.
 37. The method of claim 36, wherein the activated carbonate is bismethylsalicylcarbonate.
 38. The method of claim 1, wherein up to 50 mole % of the precursor of the carbonate source is derived from the group consisting of dicarboxylic acids, dicarboxylic acid esters, dicarboxylic acid halide or any combination thereof.
 39. The method of claim 1, wherein the inorganic catalyst is NaOH and the organic catalyst is selected from the group consisting of TMAH, TBPA, and combinations thereof.
 40. The method of claim 1, wherein the method further comprises the step of introducing a dihydric phenol to the reaction mixture within the series of process units through late monomer addition.
 41. The method of claim 40, wherein the antioxidant is introduced to the reaction mixture within the series of process units prior to the addition of dihydric phenol through late monomer addition.
 42. The method of claim 1, wherein the copolymer has a molecular weight Mw between 10,000 and 100,000 g/mole (Polystyrene standards).
 43. The method of claim 42, wherein the copolymer has a molecular weight Mw between 25,000 and 40,000 g/mole (Polystyrene standards).
 44. The method of claim 1, wherein the copolymer has a molecular weight Mw of at least 10,000 g/mole (Polystyrene standards) and the molecular weight Mw is subsequently increased to a value higher than 25,000 g/mole (Polystyrene standards) using a standard extrusion step.
 45. The method of claim 1, wherein the copolymer has a molecular weight Mw of at least 10,000 g/mole (Polystyrene standards) and the molecular weight Mw is subsequently increased to a value higher than 25,000 g/mole (Polystyrene standards) by further reaction of oligomers by means of solid state polymerization.
 46. The method of claim 1, wherein the copolymer has an end cap level of at least 80%.
 47. The method of claim 46, wherein the copolymer has an end cap level of at least 90%.
 48. A molded article formed from copolycarbonate with improved color prepared by the method comprising the steps of: i. preparing a molten reaction mixture comprising a first dihydroxy aromatic compound comprising monomer residue (a), a second dihydroxy aromatic compound comprising monomer residue (b), a carbonate source, and a polymerization catalyst, wherein monomer residue (a) is a quinone structure or a structure capable of forming a quinone structure upon oxidation, wherein monomer residue (b) is a quinone structure or a structure capable of forming a quinone structure upon oxidation different from monomer residue (a), or is,

where B is

—O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀ cycloaliphatic radical; the groups R¹ and R² are independently a hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphatic ring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a combination thereof, R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl radical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and q are both integers from 0 to 4, ii. introducing an antioxidant selected from the group consisting of hydroxycarboxylic acids, benzofuranones, phenolic antioxidants, hydroxylamines, functionalized aliphatic hydroxylamines, and substituted dibenzylhydroxylamine to the reaction mixture in an amount sufficient to result in a product copolycarbonate with improved color, iii. introducing the reaction mixture to a series of process units, iv. allowing the reaction mixture to polymerize thereby forming copolycarbonate, wherein the copolycarbonate has improved color as compared to a copolycarbonate formed in a melt process without the introduction of antioxidant, and v. forming a molded article from the copolycarbonate.
 49. A method for making a molded article formed from copolycarbonate with improved color prepared by the method comprising the steps of: i. preparing a molten reaction mixture comprising a first dihydroxy aromatic compound comprising monomer residue (a), a second dihydroxy aromatic compound comprising monomer residue (b), a carbonate source, and a polymerization catalyst, wherein monomer residue (a) is a quinone structure or a structure capable of forming a quinone structure upon oxidation, wherein monomer residue (b) is a quinone structure or a structure capable of forming a quinone structure upon oxidation different from monomer residue (a), or is,

where B is

—O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀ cycloaliphatic radical; the groups R¹ and R² are independently a hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphatic ring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a combination thereof, R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl radical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and q are both integers from 0 to 4, ii. introducing an antioxidant selected from the group consisting of hydroxycarboxylic acids, benzofuranones, phenolic antioxidants, hydroxylamines, functionalized aliphatic hydroxylamines, and substituted dibenzylhydroxylamine to the reaction mixture in an amount sufficient to result in a product copolycarbonate with improved color, iii. introducing the reaction mixture to a series of process units, iv. allowing the reaction mixture to polymerize thereby forming copolycarbonate, wherein the copolycarbonate has improved color as compared to a copolycarbonate formed in a melt process without the introduction of antioxidant, and v. forming a molded article from the copolycarbonate.
 50. The method of claim 49, wherein the polymerization catalyst is introduced to the reaction mixture according to a selected strategy, wherein the strategy is selected from the group consisting of,
 1. introducing a polymerization catalyst to the molten reaction mixture after monomer residues (a), monomer residues (b), and carbonate source are melted and prior to substantial polymerization,
 2. introducing a polymerization catalyst to the reaction mixture or monomer residues prior to melting with the proviso that residence time of the process from the start of melting until substantial polymerization has occurred is less than 4 hours, and
 3. or a combination thereof, wherein the polymerization catalyst is an inorganic catalyst, an organic catalyst, or both inorganic and organic catalyst which may be introduced separately or together.
 51. The method of claim 48, wherein the polymerization catalyst is introduced to the reaction mixture according to a selected strategy, wherein the strategy is selected from the group consisting of,
 1. introducing a polymerization catalyst to the molten reaction mixture after monomer residues (a), monomer residues (b), and carbonate source are melted and prior to substantial polymerization,
 2. introducing a polymerization catalyst to the reaction mixture or monomer residues prior to melting with the proviso that residence time of the process from the start of melting until substantial polymerization has occurred is less than 4 hours, and
 3. or a combination thereof, wherein the polymerization catalyst is an inorganic catalyst, an organic catalyst, or both inorganic and organic catalyst which may be introduced separately or together.
 52. The method of claim 1, wherein the polymerization catalyst is introduced to the reaction mixture according to a selected strategy, wherein the strategy is selected from the group consisting of,
 1. introducing a polymerization catalyst to the molten reaction mixture after monomer residues (a), monomer residues (b), and carbonate source are melted and prior to substantial polymerization,
 2. introducing a polymerization catalyst to the reaction mixture or monomer residues prior to melting with the proviso that residence time of the process from the start of melting until substantial polymerization has occurred is less than 4 hours, and
 3. or a combination thereof, wherein the polymerization catalyst is an inorganic catalyst, an organic catalyst, or both inorganic and organic catalyst which may be introduced separately or together. 